For efficient operation, modern lumber machining systems require substantially continuous processing of relatively large volumes of lumber. Accordingly, machining devices, such as planers, capable of machining 2000 linear feet of lumber or more per minute have been developed. In order to fully utilize such machining devices, however, lumber delivery systems must be capable of providing such machining devices with lumber at the relatively rapid rate at which the machining device is processing the lumber.
Typical lumber delivery systems have been comprised of three distinct portions. The first portion generally consists of a number of substantially parallel chain conveyors for receiving lumber, typically from a storage bin, and for hauling the pieces of lumber for ultimate delivery to the machining device. These chain conveyors typically move the pieces of lumber in a first direction substantially perpendicular to the predetermined longitudinal machining path of the machining device which is the direction in which lumber moves through the machining device.
The second portion of such typical lumber delivery systems includes a number of machine rolls for receiving the lumber from the chain conveyors and for moving the lumber toward the machining device and a line bar. Such machine rolls are generally metallic cylinders which may have a relatively slick exterior surface. The line bar is typically a metallic beam having a substantially planar front surface for aligning the pieces of lumber with the predetermined longitudinal machining direction. A number of spaced apart rollers are generally inset into the planar front surface of the line bar for facilitating longitudinal movement of lumber along the line bar.
A number of rolls, such as pineapple rolls, are typically mounted above the line bar for both moving the pieces of lumber toward the machining device and holding the pieces of lumber against the line bar such that the pieces of lumber remain aligned with the machining device. The rotation of the pineapple rolls both move and hold the pieces of lumber due, in part, to a raised ridge spirally wound about the rolls for contacting the lumber. The spirally wound ridge is positioned such that rotation of the roll urges the piece of lumber with which it is in contact both toward the machining device and the line bar.
The third portion of such typical lumber delivery systems includes a bridge portion for accelerating the lumber to speeds greater than the predetermined longitudinal speed at which the machining device processes the lumber. The bridge is generally comprised of a plurality of machine rolls for carrying the lumber, and one or more overlying pinch rolls or speedup rolls for contacting an upper surface of the lumber and, in combination with the plurality of machine rolls, accelerating the lumber. The bridge also typically includes a guide bar aligned with the line bar for maintaining alignment of the lumber during its acceleration.
Such lumber delivery systems typically move the pieces of lumber in a first direction substantially perpendicular with the longitudinal machining path of the machining device with the chain conveyors; align the lumber with the longitudinal machining axis of the machining device with the line bar; and subsequently accelerate the lumber to substantially match the predetermined longitudinal speed of the machining device.
In addition to rapid processing speeds, modern lumber applications generally require the manufacture of high quality lumber having relatively few, if any, defects such as chips, indentions, splintered edges or cracks. Further, in the limited applications in which lumber with defects, or inferior grades of lumber, may be utilized, the prices paid for such inferior grades of lumber are markedly less than those paid for the higher quality lumber.
Typical lumber delivery systems, as previously described, are relatively susceptible to damaging lumber. For example, in order to deliver lumber at the relatively high processing speeds at which modern machining devices operate, the lumber must be rapidly delivered, aligned and accelerated. Movement of the lumber along the line bar by the overlying rolls, such as pineapple rolls, may damage the lumber's surface since such rolls must grip the lumber relatively tightly in order to rapidly accelerate the lumber.
Such lumber delivery systems also typically included a gate disposed between the machine rolls or the line bar and the bridge portion. The gate is generally a metallic bar positioned to only allow one piece of lumber to pass to the bridge portion at a time. The chain conveyors of such lumber delivery systems, were not generally synchronized with the processing speed of the machining device, such that a number of pieces of lumber could accumulate at the gate awaiting passage to the bridge portion. The lateral contact between the accumulated lumber and the frictional forces generated therebetween increases the drag which must overcome in order to move the piece of lumber into the machining device. Such additional drag is especially apparent in modern machining devices which operate relatively rapidly.
In addition, the relatively rapid acceleration by the bridge to the longitudinal processing speed of the machining device generally butts the leading edge of the accelerated piece of lumber against the trailing end of the piece of lumber being machined. This abutment may result in splintering or chipping of the ends of the lumber.
As the speeds at which modern machining devices process lumber have increased, the demands on the lumber delivery systems operating in conjunction with such rapid machining devices have correspondingly risen. Notwithstanding the increasing processing speeds, the delivery of the lumber must not damage the lumber or introduce defects since the quality of the lumber must be maintained.